SOLAR AND PLANETARY EVOLUTION.* 



EvERYTiiixG of which Ave have any knowledge is the re- 

 sult of groAvth or progress, in one Avay or another, accord- 

 ing to laAv. I suppose that no reasonable person, who is ac- 

 ([uainted Avith the facts, Avould pretend that the earth or 

 the universe is any less the result of a regular process of 

 development than a tree. 



The question before us is, Hoav did the world begin ? How 

 were the heavens framed ? Any ansAver that may be made to 

 this question must take into account Avhat, broadly speaking, 

 may be termed the nebular theory. But Ave need not confine 

 (jurselves to the consideration of the theory of Laplace. I 

 speak just noAV of a nebulous beginning in a general sense, 

 Avithout special reference to any particular hypothesis. 

 What we Avant to get, first of all, is a clear conception of 

 hoAV the solid earth, the sun, and all the substantial bodies 

 by which Ave are surroimded, Avere once nebulous masses, as 

 thin as air. 



Perhaps Ave can best get at it in this Avay. Suppose Ave 

 could take a puff of steam just as it came from the boiler, 

 and remove it, freed from all external influences, into space. 

 What Avouid happen ? At first, perhaps, oAving to its great 

 heat, the steam would be invisible. But the intense cold 

 of surrounding space Avould cause it to radiate its heat, and 

 it Avould condense until it became visible as a cloud of vapor. 

 The two great constructive forces of the universe, heat and 

 gravitation, Avould carry on a contest in the little puff of 

 steam ; heat y)ushing outAvard, gravitation draAving iuAvard. 

 But gravitation is the more persistent force, and as the heat 



♦ Synopsis, from steno{!;raiiher's notes, corrected liy the lecturer. rorvincHT. 

 1889, by The New l(le;il TnblishinK f'oiiii)any. 



The thanks of the I'ublishcrs, and of the Brooklyn Ethical Association, are 

 due to Messrs. T). Appleton \' Company for the use of the illustrations on papes 

 .59, 63, 64, 6.-., 66, 68 and (19. 



The cuts illustrating Laplace's theory and Faye's hypothesis were kindly fur- 

 nished by Mr. Serviss — the former liaving been devised by Professor (ieorsre 

 AA'. f'oakley, ff)r his lecture on "The Nebular Hypothesis of Laplace," read be- 

 fore the Aiiicricnn Astronomical Society. 



